1. Field of the Invention
The present invention pertains to a light emitting diode with high luminance and method therefor, and specially to a light emitting diode having a selectively highly-doped low resistant layer of InGaAlP.
2. Description of the Related Art
In a semiconductor made of group III or V composite, for an InGaAlP whose energy gap less than that of nitride, when the ratio of aluminum to gallium in the active region of the light emitting element is changed, the light wavelength varies from 680 nm to 550 nm. Further, since the lattice constant of InGaAlP can match the GaAs substrate perfectly, InGaAlP is suitable for the light emitting element used for visible light region.
As shown in FIG. 1, the Structure of a conventional InGaAlP light emitting diode is formed by growing a multi-layered epitaxy layer on a n type GaAs light-absorbing substrate 10. First, a n-InGaAlP confining layer 11 is grown on the GaAs substrate 10, and then a p-InGaAlP confining layer 13 is grown on an active layer 12 such that a double hetrostructure is formed. The light wavelength of the light emitting diode is determined by the ratio of aluminum to gallium in the active layer 12. An increase in the content of aluminum in the active layer may shorten the light wavelength of the light emitting diode. Meanwhile, the content of aluminum in the confining layers 11, 13 outside the active layer 12 must be greater than that of aluminum in the active layer 12 such that the carriers may be not only effectively injected into the active layer 12 but also prevent the light emitted from the active layer 12 from being absorbed by the confining layers 11 and 13. Besides, the light emitting surface of the diode is coated with a front surface metal electrode 14 and coated with a back surface metal electrode 15 on the surface of the GaAs substrate 10 on which the expiate layer is not formed.
Generally speaking, with the exception of the combination efficiency of the electron and the electric hole, the major factor for determining the light emitting efficiency of a light emitting diode is whether the current on the front surface electrode 14 can be effectively distributed to the boundary of grains such that the light can be uniformly produced from the p-n junction. If the p-type confining layer 13 is too resistant to effectively distribute the current, the current will flow from the front surface electrode 14 to the back surface electrode 15, causing current jamming such that the current can not be spread effectively and that most of the generated light can not emit due to the blocking of the opaque front surface electrode 14 or the light emitting efficiency thereof is reduced because the generated light is reflected by the metal electrode 14 and absorbed by the substrate. The conventional InGaAlP light emitting diode has the above drawbacks. This is because the impurity concentration of the p-type InGaAlP confining layer 13 is generally below 1xc3x971018 cmxe2x88x923 and the hole mobility thereof is merely 10xcx9c20 cm2xc2x7V/sec, which forms the resistivity 0.5xcexa9-cm. The resistivity is so high that the lateral current can not be spread over the whole grain. To solve this problem, as shown in FIG. 2, a conventional technique, such as U.S. Pat. No. 5,008,718 develops a different structure. The structure as illustrated in FIG. 2 is formed by growing a semiconductor window layer 16 differing from the InGaAlP layer on the p-type InGaAlP confining layer 13. The window layer is characterized by its low resistivity, perfect conductivity, and energy gap greater than that of the active layer 12. Thus, the semiconductor window layer 16 does not absorb the light emitted from the p-n junction. The materials suitable for the semiconductor window layer 16 include GaAlAs, GaAsP, and GaP, etc. The optimum thickness for the window layer 16 ranges from five to tens of micrometers. However, the lattice constants of GaAsP and GaP do not match with those of the GaAs substrate and the InGaAlP layer 13, causing a large amount of dislocation on the growing interface and disadvantageously affecting the opto-electrionic characteristics of the light emitting diode. As shown in FIG. 3, another structure of the conventional technique, such as U.S. Pat. No. 5,048,035 is characterized by additionally forming a current blocking layer 17 and bragg reflector layer 18 with a current spreading layer or window layer 19 made out of GaAlAs. The diode structure of ""035 patent is so configured that the current injected from the front surface electrode 14 is influenced by the current blocking layer 17 to be effectively distributed to the current spreading layer 19.
To avoid the above-mentioned problems encountered in the prior art, the present invention provides a novel high luminance InGaAlP light emitting diode having the following advantages:
(1) A highly doped low resistant layer is utilized as a mechanism for distributing the current.
(2) A current blocking layer is not needed.
(3) Doping sources alternatively used for growing the current blocking layer are not needed.
The light emitting diode of the present application comprises a first metal electrode, a substrate, a first confining layer, a n active layer, a second confining layer, a selectively highly doped low resistant layer, a multi-layered low light-absorbing current spreading layer and a second metal electrode and is characterized in that it is accomplished by the processing of two times epitaxially growing, one time masking and etching. The first epitaxially growing is that sequentially growing a first confining layer, an active layer, a second confining layer and a selectively highly-doped low resistive layer, and that a needed portion of selectively highly-doped low resistive layer remains after the selectively highly-doped low resistive layer is processed by masking and etching. The second epitaxially growing is that the chip of the InGaAlP light emitting diode according to he present application is grown a multi-layered low light-absorbing current spreading layer by an organic-metal vapor phase epitaxy (OMVPE) in the epitaxy system and coated with a first metal electrode and second metal electrode, thereby accomplishing the fabrication of the light emitting diode with high luminance of the present application.
According to a preferred embodiment of the present application, a p type highly-doped low resistive layer 20 is grown on a p type InGaAlP confining layer 13, and then is masked and etched to expose a portion of the p-InGaAlP confining layer 13. Because, the impurity concentration of the InGaAlP confining layer is less than 1xc3x971018 cmxe2x88x923, the exposed portion as mentioned above is the p-InGaAlP confining layer 13 having higher resistivity, thus rendering the current lowing towards the p type highly-doped low resistive layer 20 which remains by selectively etching, thereby achieving the current spreading.
Another object of the present application is to provide a method for manufacturing a light emitting diode of high luminance having a highly-doped low resistive layer by growing a p-type highly-doped low resistive layer 20 on an InGaAlP double hetrostructure, wherein the material of the layer 20 may be GaAs, GaAlAs, GaAsP, and GaP or any semiconductor material whose impurity concentration is greater than 1xc3x971018 cmxe2x88x923, and by the processing of the masking and etching to expose a p-type InGaALP confining layer 13 having greater resistivity so that the current flows towards the p-type highly-doped low resistive layer 20 to achieve the current spreading, thereby enhancing the light emitting efficiency of the light emitting diode.